Steerable chassis for work vehicle

ABSTRACT

A steerable chassis for work vehicle, having a coupling with a hinge that has a vertical axis in order to act as a steering system and an articulation that has a horizontal axis in order to ensure greater freedom of torsional oscillation of that chassis. The chassis has a device for locking the articulation, as selected by the operator, in order to increase the torsional rigidity of the chassis when required.

The present invention relates to a steerable chassis for a work vehicle.

A steering mechanism with two steerable wheels is generally used inorder to change the direction of travel of a work vehicle or of anyother kind of vehicle; in most cases, the steerable wheels are the frontwheels, whereas in some cases, in some work vehicles such as fork-lifttrucks, cranes, et cetera, the rear wheels are used.

For some work vehicles, especially vehicles that are not too large, suchas small bulldozers, cranes, excavators, fork-lift trucks et cetera, itis advantageous to use a particular steerable chassis to change thetravel direction of the vehicle instead of using a steering mechanismwith steerable wheels.

These vehicles have a chassis that is substantially divided into tworigid portions that have no steerable wheels: a front chassis portion,which supports the front wheel axle, and a rear chassis portion, whichsupports the rear wheel axle.

The front and rear chassis portions are connected by means of anarticulated coupling, which in a simple embodiment is substantiallyconstituted by a hinge that has a vertical axis, for example of thefifth-wheel type.

Steering is achieved by acting on suitable actuation members that varythe angle formed by the longitudinal axes of the two chassis portionswith respect to the fulcrum constituted by the hinge from a maximumvalue of 180°, for straight travel, to a minimum value, to which maximumsteering curvature corresponds.

Substantially, during steering, the chassis of the vehicle literally“bends” at the hinge, thus allowing the operator to change the directionof travel of the vehicle.

Since this kind of vehicle usually lacks wheel suspensions, it isparticularly uncomfortable for the operator, especially when travelingover bumpy roads.

In order to increase travel comfort, therefore, it has been thought toadopt, instead of the simple articulated coupling described above, acomplex coupling that includes a hinge that has a substantially verticalaxis, in order to allow the vehicle to steer, combined with anarticulation whose axis is substantially parallel to the longitudinalaxis of the vehicle.

A degree of freedom is thus added to the relative motion of the twochassis portions, because in addition to “bending”, the chassis portionsare capable, by means of the articulation, of “oscillating” with respectto each other relative to an axis that is substantially parallel to theaxis of the vehicle.

The axles of the front and rear wheels can thus assume a differentinclination with respect to the ground, accordingly eliminating thetorsional rigidity of the chassis and consequently increasing its travelcomfort.

This solution is certainly advantageous for improving comfort of thevehicle during travel, but it can lead to drawbacks when the vehicle isinstead stationary and is working, because it decreases its stability.

The work vehicles being considered are in fact used to lift loads ofsome kind by means of a suitable implement installed at the front of thevehicle, such as a fork lift in the case of a fork-lift truck, a bucketor an excavator arm in the case of an excavator, et cetera.

During lifting, if the center of gravity of the load accidentally fallsoutside the vertical, the oscillating motion of the two chassis portionsabout the articulation produced by the imbalance of weights may cause adestabilization of the vehicle that generates in certain cases a severerisk of lateral tipping of the vehicle.

The aim of the present invention is to provide a steerable chassis for aworking vehicle that overcomes the drawbacks of the cited known art.

An object of the invention is to provide a steerable chassis that allowsto increase the torsional rigidity and stability of the vehicle duringwork when the vehicle is not moving.

A further object is to provide a steerable chassis that ensures greattravel comfort when the vehicle is moving.

This aim and these and other objects that will become better apparenthereinafter are achieved by a steerable chassis for working vehicle,comprising two chassis portions, respectively a front portion and a rearportion, which are mutually connected and can rotate with respect toeach other about a substantially vertical axis and about a substantiallyhorizontal axis that is parallel to the longitudinal axis of the workingvehicle, the steerable chassis being characterized in that it comprisesa device for locking the relative rotation of the chassis portions aboutthe substantially horizontal rotation axis.

Further characteristics and advantages of the invention will becomebetter apparent from the following detailed description of preferred butnot exclusive embodiments thereof, illustrated by way of non-limitingexample in the accompanying drawings, wherein:

FIG. 1 is a side elevation view of a working vehicle with steerablechassis;

FIG. 2 is a perspective view of the rear chassis portion;

FIG. 3 is a perspective view of the articulation locking device;

FIG. 4 is a partially sectional side elevation view of the articulation;

FIGS. 5 and 6 are two views of the operation of the articulation lockingdevice.

With reference to the cited figures, a steerable chassis for a workingvehicle is generally designated by the reference numeral 100.

The chassis comprises two chassis portions, respectively a rear portion50 and a front portion 60.

An implement 70 for lifting a load of a certain type is installed at thefront of the front chassis portion 60.

The rear chassis portion 50 and the front chassis portion 60 aremutually connected centrally by virtue of a complex coupling 1, whichallows the chassis portions 50 and 60 to rotate with respect to eachother about a substantially vertical axis 25 and about a substantiallyhorizontal axis 20 that is parallel to a longitudinal axis 30 of thevehicle 100.

As shown in FIG. 2, the coupling 1 comprises a hinge 2 that has avertical axis 25 and provides an articulated connection between the rearchassis portion 50 and the front chassis portion 60, thus steering thework vehicle.

The coupling 1 further comprises an articulation 3, the free rotationaxis of which coincides with the horizontal axis 20.

The articulation 3 is constituted by a shaft 4 that is welded to thehinge 2, and is therefore rigidly coupled to the front chassis portion60, and by a bush 5, which is welded externally to the structure of therear chassis portion 50 and is therefore rigidly coupled thereto.

The shaft 4 is pivoted in the bush 5 with the interposition of twoantifriction bearings 13 and 14 between them.

The shaft 4 is hollow in order to reduce weight and cost of material.

As shown in FIG. 4, the shaft 4 and the bearings 13 and 14 are kept inan axial position with respect to the bush 5 by a lateral containmentring 15, which is welded to one end of the shaft 4, and by a threadedring 16 that can be screwed firmly onto a female thread that is formedon the other end of the shaft 4.

A washer 17, for preventing unscrewing, is interposed between theshoulder of the bearing 14 and the ring 16.

According to the invention, the chassis comprises a device 6 for lockingthe relative rotary motion of the two chassis portions 50 and 60 aboutthe horizontal axis 20.

In practice, the device 6 acts by locking the articulation 3.

The device 6 comprises a rocker member 7, which is fixed axially to theshaft 4, and as such is rigidly coupled to the front chassis portion 60in its oscillation with respect to the axis 20.

The rocker member 7 is fixed to the end of the shaft 4 that liesopposite the hinge 2, with the bush 5 in an intermediate positionbetween the rocker 7 and the hinge 2.

The rocker 7 is accommodated within the structure of the rear chassisportion 50 and is therefore hidden from view.

The means for fixing the rocker member 7 to the shaft 4 consists ofthree stud bolts 10, which are axially screwed into the head of theshaft 4.

The shaft 4 comprises a hexagonal protruding member 11 that is coupledthereto with interference at its cavity.

In order to improve the rigidity and safety of the connection betweenthe rocker 7 and the shaft 4, especially from a torsional standpoint,the hexagonal member 11, by protruding from the shaft 4, is accommodatedin a complementary hexagonal recess 12 formed in the rocker 7.

When the operator chooses to do so, the rocker member 7 can be locked ina substantially horizontal position by virtue of a hydraulic actuationmeans.

The rocker member 7 is in fact symmetrical and includes twosubstantially horizontal arms, designated by the reference numerals 7 aand 7 b, which abut, as shown in FIG. 5, against the movable end of twohydraulic pistons, designated respectively by the reference numerals 8 aand 8 b, which have a substantially vertical axis, when the pistons 8 aand 8 b are simultaneously in the raised position.

The hydraulic cylinders 9 a and 9 b that correspond to the pistons 8 aand 8 b are fixed to the base of the rear chassis portion 50 by means ofscrews.

The cylinders 9 a and 9 b are arranged symmetrically with respect to theaxis 20 and so that each one of the movable ends of the pistons 8 a and8 b coincides vertically and can abut against the respective end portionof the arms 7 a and 7 b.

The region of contact between the pistons 8 a and 8 b and the arms 7 aand 7 b is defined by a substantially horizontal supporting surfaceformed in the end portions of the arms 7 a and 7 b.

The hydraulic cylinders 9 a and 9 b include a hydraulic circuit, shownin FIG. 4, by acting on which the operator is capable of pressurizingthe hydraulic liquid in the cylinders, thus producing an upward thrustof equal intensity of the pistons 8 a and 8 b.

The elongation of the movable end of the pistons 8 a and 8 b is thesame.

The operation of the locking device 1 is clearly shown in FIGS. 5 and 6.

In FIG. 6, the pistons 8 a and 8 b are not raised simultaneously,because the hydraulic liquid is not pressurized.

In this case, the rocker member 7 can assume any inclination withrespect to the base of the rear chassis portion 50, and accordingly theangular oscillation about the axis 20 of the shaft 4 with respect to thebush 5 is not prevented.

Accordingly, the front chassis portion 60 and the rear chassis portion50 can “oscillate” with respect to each other.

This is the configuration that is generally kept during travel of thevehicle in order to increase its travel comfort by way of the relative“oscillation” of the chassis portions.

FIG. 5 instead illustrates the configuration assumed by the device 6when one wishes or needs to increase the stability of the vehicle, suchas for example when it is standing still and lifting a load.

In this case, by means of a suitable control, the operator activates thesimultaneous lifting of the pistons 8 a and 8 b against the horizontalarms 7 a and 7 b of the rocker 7.

The upward thrust forces produced by the pistons 8 a and 8 b produce twomoments that act on the rocker 7 and are identical and opposite, thusforcing the rocker 7 to assume and maintain a perfectly horizontalattitude, with the rocker 7 parallel to the base of the rear chassisportion 50.

Accordingly, the “oscillation” with respect to the articulation of thetwo chassis S portions is prevented, accordingly increasing considerablythe torsional rigidity of the steerable chassis.

In practice it has been found that the invention achieves the intendedaim and objects, a steerable chassis for a working vehicle having beenprovided in which it is possible to increase the torsional rigidity ofthe chassis.

The chassis is particularly suitable for wheeled and small workvehicles, mainly having a weight of less than two tons.

The chassis according to the invention is susceptible of numerousmodifications and variations, within the scope of the appended claims.All the details may be replaced with other technically equivalentelements.

The materials used, as well as the dimensions, may be any according torequirements and to the state of the art.

1. A steerable chassis for a work vehicle, comprising two chassisportions, respectively a front portion and a rear portion, which aremutually connected and can rotate with respect to each other about asubstantially vertical axis and about a substantially horizontal axisthat is parallel to the longitudinal axis of the working vehicle, saidsteerable chassis further comprising a device for locking the relativerotation of said chassis portions about said substantially horizontalrotation axis.
 2. The chassis according to claim 1, wherein said devicecomprises a rocker member that can be rocked by an actuation means. 3.The chassis according to claim 2, wherein said actuation means is anhydraulic actuation means.
 4. The chassis according to claim 3, whereinsaid hydraulic actuation means comprises at least one hydraulic cylinderassociated with a piston.
 5. The chassis according to claim 1, whereinsaid two chassis portions, respectively the front portion and the rearportion, are connected by virtue of a complex coupling that comprises ahinge, whose rotation axis coincides with said substantially verticalaxis, and an articulation, whose rotation axis coincides with saidsubstantially horizontal axis, said articulation being comprised of ashaft that is rigidly coupled to the front chassis portion and ispivoted in a bush that is rigidly coupled to the rear chassis portion.6. The chassis according to claim 5, wherein said rocker member isrigidly coupled to said shaft and is provided with two substantiallyhorizontal arms, each of which can be abutted against the movable end ofa hydraulic piston that has a substantially vertical axis when saidpiston is in the raised position, the hydraulic cylinder thatcorresponds to each piston being rigidly coupled to said rear chassisportion.
 7. The chassis according to claim 6, further comprising a meansfor coupling said rocker member to said shaft, said means consisting ofstud bolts that are screwed with an axis that is parallel to the axis ofsaid shaft.
 8. The chassis according to claim 6, wherein said shaftcomprises a hexagonal protruding member, which abuts in a correspondinghexagonal recess that is formed axially in said rocker.
 9. The chassisaccording to claim 6, wherein said rocker member is symmetrical, saidhorizontal arms extending symmetrically and at right angles with respectto the axis of said shaft.
 10. The chassis according to claim 6, whereineach one of said substantially horizontal arms comprises an end portionthat is provided with a substantially horizontal supporting surface formaking contact with the movable end of said corresponding hydraulicpiston when said piston is in the raised position.
 11. The chassisaccording to claim 6, wherein said pair of hydraulic cylinders, one foreach of the two arms of said rocker member, are fixed to the base ofsaid rear chassis portion by means of screws.
 12. The chassis accordingto claim 6, wherein the movable end of each one of said pistons has thesame elongation.